Low RCS Antennas

The level of the backscattered field of an object when hit by an electromagnetic wave is an important parameter in a wide range of applications. For example, in the context of radio-frequency identification (RFID), the modulated backscattering operated by the chip is of utmost importance in recovering the information provided by the tag placed in the interrogated item and the level of reradiated energy is such a desirable feature that a great effort is devoted towards its enhancement.
However, in other situations the electromagnetic echo is an undesired side effect which has fostered during the last decades an effort aimed to consistently reduce it. This last scenario may refer to a radar target, that wants to be as unobservable as possible. In this framework, the Radar Cross Section (RCS) provides a meaningful description of the energy backscattered by the object.

A well-known technique adopted to decrease the RCS of aircrafts or other cumbersome platforms consists in shaping the object surfaces in order to reflect the scattered energy away from the detecting receiver. One of the main obstacles in achieving the Radar Cross Section Reduction (RCSR) is determined by the presence of an antenna on the target. Therefore an antenna can be tilted or have its shape modified to deflect the probing wave and causing the stronger reflection at directions where the RCS is less significant than at others, typically out of the broadside. A similar objective can also be accomplished by employing a bandpass Frequency Selective Surfaces (FSS) radome that, being totally reflecting, deviates elsewhere the interrogating waves outside the antenna operating band.
FSSs can be also employed as a frequency selective ground plane to reduce the RCS of a reflectarray, array of monopoles or even printed microstrip patch arrays [1]. The objective of the latter designs is to provide a perfect electric ground plane within the working bandwidth of the radiating device whereas exhibiting pass-band characteristics in other frequency bands thus being transparent to the impinging wave. In all the aforementioned cases the purpose is to forbid the energy from coming back to the detecting device thus achieving a monostatic RCS reduction and avoiding the target localization.